Structure Property Analysis of the Solution and Solid-State Properties

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Structure Property Analysis of the Solution and SolidState Properties of Bistable Photochromic Hydrazones Baihao Shao, Hai Qian, QUAN LI, and Ivan Aprahamian J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b03932 • Publication Date (Web): 03 May 2019 Downloaded from http://pubs.acs.org on May 3, 2019

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Journal of the American Chemical Society

Structure Property Analysis of the Solution and Solid-State Properties of Bistable Photochromic Hydrazones Baihao Shao,† Hai Qian,† Quan Li, Ivan Aprahamian* Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA. KEYWORDS. Hydrazones, photochromic compounds, bistability, emission toggling, molecular switches

ABSTRACT: The development of new photochromic compounds, and the optimization of their photophysical and switching properties are prerequisites for accessing new functions and opportunities that are not possible with currently available systems. To this end we recently developed a new bistable hydrazone switch that undergoes efficient photoswitching and emission ON/OFF toggling in both solution and solid-state. Here, we present a systematic structure-property analysis using a family of hydrazones, and show how their properties, including activation wavelengths, photostationary states (PSSs), photoisomerization quantum yields, thermal half-lives ( 1/2), and solution/solid-state fluorescence characteristics vary as a function of electron donating (EDG) and/or withdrawing (EWG) substituents. These studies resulted in the red-shifting of the absorption profiles of the Z and E isomers of the switches, while maintaining excellent PSSs in almost all of the compounds. The introduction of para-NMe2, and/or para-NO2 groups improved the photoisomerization quantum yields, and the extremely long thermal half-lives (tens to thousands of years) were maintained in most cases, even in a push-pull system, which can be activated solely with visible light. Hydrazones bearing EDGs at the stator phenyl group are an exception and show up to 6 orders of magnitude acceleration in 1/2 (i.e., days) because of a change in the isomerization mechanism. Moreover, we discovered that a para-NMe2 group is required to have reasonable fluorescence quantum yields in solution, and that rigidification enhances the emission in the solid-state. Finally, X-ray crystallography analysis showed that the switching process is more efficient in the solid-state when the hydrazone is loosely packed.

INTRODUCTION Photochromic compounds,1 may they be azobenzenes,2 stilbenes,3 spiropyrans,4 or diphenylethenes5 form an integral part of the tool-set available to molecular machinists.6 Throughout the decades, these triggers enabled practitioners to design adaptive materials,7 and develop drugs,8 catalysts,9 artificial molecular machines and motors,10 in addition to other systems that can be turned ON/OFF using the high spatial and temporal resolution of light. Accessing these functions necessitated the optimization of the properties and capabilities (e.g., photostationary states (PSSs), quantum yields ( ), thermal relaxation half-lives ( 1/2), absorption/activation wavelengths, emission toggling, etc.) of these light switches, which in turn greatly enhanced the proliferation of these tools in diverse areas of research. Nonetheless, there is yet a need to pinpoint a system and/or families of switches that encompasses all the desirable characteristics of photochromic compounds, i.e., ease of synthesize, high thermal stability, @( photoconversion, high photostability, broad and tunable activation wavelengths, switching in both solution and solid-state, large geometrical and dipole changes, biocompatibility, switching in aqueous media and serum, resistance to glutathione reduction, etc. Driven by a desire to overcome these obstacles, and the onset of new applications and

possibilities, such as photopharmacology,8 the past decade witnessed a surge in the design of new photochromic scaffolds, including but not limited to indigoids,11 hydrazones,12 acylhydrazones,13 azo-BF2 complexes,14 heterophenyl azo dyes,15 imidazole dimers,16 and donoracceptor stenhouse adducts.17 These systems expand the tool-kit available to the scientific community, and will open the way for new opportunities, once their properties are well-understood and optimized. Scheme 1. The structures of the photochromic hydrazone switches. Rotor and stator designations are arbitrary. rotor

O

R2

O N

N

stator R1

H

1 R1 = H, R2 = H 2 R1 = H, R2 = p-NMe2 3 R1 = H, R2 = m-NMe2 4 R1 = H, R2 = p-OMe 5 R1 = H, R2 = p-NO2 6 R1 = CN, R2 = H 7 R1 = NO2, R2 = H 8 R1 = OMe, R2 = H 9 R1 = NMe2, R2 = H 10 R1 = NO2, R2 = p-NMe2

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Our interest in developing hydrazone-based molecular switches 18 recently led us to the discovery of a new family of hydrazone-based bistable photochromic switches having half-lives ( 1/2) as long as 5,300 years. 19 We subsequently used these switches in polymer actuation,20 and controlling the self-assembly of liquid-crystals.21 In both these instances the bistability of the switch gave us access to hitherto underexplored properties – multistep/state actuation and order to higher order phase transitions (i.e., from cholesteric to Smectic A) – thus showcasing the benefits of designing new switchable systems. Next, we showed that substituting the stator phenyl moiety with a para-dimethyl amine (NMe2) group (2) yields an emissive compound whose fluorescence could be toggled ‘ON’ and ‘OFF’ both in the solution and solid-state.22 Herein, we report on a systematic study of the solution and solid-state switching and fluorescence emission properties of this new class of photoswitches. The structure property analyses (Scheme 1) were conducted by derivatizing the rotor (red) and stator (blue) phenyl groups with electron-withdrawing (EWGs) and electron-donating groups (EDGs). These modifications allowed us to assess the substituent effect on the photostationary states and quantum yields of the switch, tune the half-life from thousands of years to days, and redshift the activation (Figure 1) and emission wavelengths of the hydrazones. Moreover, we made strides in showing that emission in these systems indeed stems from excitedstate intramolecular proton transfer (ESIPT)-coupled charge transfer (CT). Finally, analysis of X-ray data corroborated the hypothesis that loose packing is responsible for both the switching of the systems and their emission in the solid-state.

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our discussion on the EWG containing derivatives. The absorption maxima (#max) of the Z and E forms of the paraCN substituted hydrazone 6 are almost identical to those of 1 (Table 1). Conversely, para-NO2 substitution on either the rotor (5) or stator (7) phenyl ring induces a ca. 20 nm red-shift in the #max of the Z isomers. This unusual effect could be attributed to the formation of a “quinoid” form in 7 which leads to the extension of the -system through resonance between the hydrazone NH nitrogen and the NO2 group,23 and a more stabilized LUMO (i.e., narrower HOMO-LUMO gap) in 5. The red-shift (33 nm) is retained in the E isomer of 7 relative to 1 as the effect stems from the stator part, which is not effected by isomerization, while a 20 nm blue-shift is observed in 5-E, which is the expected outcome upon NO2-substitution, and loss of Hbonding induced planarity of hydrazone skeleton. All three hydrazones have excellent PSSs (>90%; 410/442 nm irradiation) going from Z to E (Table 1), thanks to the wellseparated absorption bands of the two isomers (Figure 2b, Figures S23 and S26 in the Supporting Information). The PSSs for the reverse process are also very high (> 80%; 340/365 nm irradiation) for compounds 6 and 7, while for 5 a PSS340 of 52% was measured because irradiation was done very close to the isosbestic point.24 Good quantum yields (>10%) were measured for both isomerization directions in 5 and 7, and particularly high (35.3%) for the Z E isomerization process in 7. Compound 6 on the other hand exhibits lower values ( Z E = 4.1 0.1% and E Z = 5.1 0.3%). All three compounds exhibit good fatigue resistance as well (Figure 2c and Figures S24 and S27). (a)

RESULTS AND DISCUSSION

1-Z 7-Z 9-Z 10-Z

R1 = H, R2 = H R1 = NO2, R2 = H R1 = NMe2, R2 = H R1 = NO2, R2 = NMe2

R2

Synthesis: Hydrazones 3, 4, 6, 7, 8 and 10 were synthesized in good yields (52-83%) using a facile onestep procedure starting from appropriately substituted hydrazines and -ketoesters (Scheme S1 in the Supporting Information). Hydrazones 119a and 222 were synthesized in a similar manner and used as reference compounds. While, compounds 5 and 9 were prepared (49 and 78%, respectively) using a one-step diazo coupling reaction (Scheme S2 in the Supporting Information). The Z isomer was separated (after column chromatography) as the major configurational isomer in all reactions. This assignment was corroborated using the chemical shift of the intramolecular H-bond between the NH proton and carbonyl oxygen that resonates between 11.5 13.0 ppm in toluene-d8. All the new compounds were fully characterized using NMR spectroscopy, high-resolution mass spectrometry, and X-ray crystallography (See Figures S1 16 and S74 80 in the Supporting Information). Photophysical Properties: The UV spectra of the Z and E isomers (obtained after irradiation at appropriate wavelength or by data extrapolation) of compounds 3-10 were measured (or derived) in toluene. We will first focus

O O N

N

H

Z R1

(b)

1-E 8-E 7-E 10-E

R1 = H, R2 = H R1 = OMe, R2 = H R1 = NO2, R2 = H R1 = NO2, R2 = NMe2 R2

O O H

N

N

E R1

Figure 1. (a) Normalized UV-Vis spectra for the Z isomers of hydrazones 1, 7, 9 and 10 in toluene; (b) Normalized UV-Vis spectra for the E isomers of hydrazones 1, 7, 8 and 10 in toluene.

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Journal of the American Chemical Society Table 1. Photophysical data for compounds 1 10 in toluene. Hydrazone

#max (nm) / %a

PSS @

irr

(nm)

Z

E

Z E

E Z

1b

367 / 18300

334 / 18000

7.5 0.1 %

10.6 0.2 %

95 % of E @ 410

2(p-NMe2)c

395 / 14500

343 / 13800

32.0 0.9 %

14.7 1.0 %

> 99 % of E @ 442

82 % of Z @ 340

3(m-NMe2)

366 / 19200

331 / 19300

16.2 0.5 %

10.7 0.5 %

> 99 % of E @ 410

54 % of Z @ 340d

4(p-OMe)

376 / 21100

330 / 19500

4.7 0.1 %

9.1 0.6 %

98 % of E @ 410

84 % of Z @ 340

5(p-NO2)

392 / 24900

314 / 13500

11.7 0.3 %

12.6 1.3 %

92 % of E @ 442

52 % of Z @ 340d

6(p-CN)

368 / 26300

333 / 26600

4.1 0.1 %

5.1 0.3 %

> 99 % of E @ 410

86 % of Z @ 340

7(p-NO2)

391 / 26800

366 / 24300

35.3 2.1 %

11.4 0.1 %

98 % of E @ 442

82 % of Z @ 365

8(p-OMe)

383 / 17200

351 / 13900

5.3 0.1 %

9.5 0.5 %

93 % of E @ 442

88 % of Z @ 340

27 % of E @ 480

-e

> 99 % of E @ 480

96 % of Z @ 375f

9(p-NMe2)

410 / 17800

398 / 11900

65.4 6.1 %

-e

10(p-NMe2, p-NO2)

435 / 18300

384 / 17600

46.2 4.2 %

7.4 1.1 %f

76 % of Z @ 340

The extinction ( @( (%) is calculated in L mol–1 cm–1; b Ref 19a; c Ref 22; d Band overlap and hence no access to optimal switching wavelength; e Because of the poor band separation, an optimal irradiation wavelength was not found to initiate the E Z isomerization process; f = 19.4 0.6 % and PSS = 90 % of Z when 410 nm light is used for the E O Z process.

a

Hydrazones 4, 8 and 9, having EDGs at the para-position of the stator or rotor phenyl groups all show a red-shift in the #max of their Z isomer relative to 1, which also holds for the E isomer of 8 and 9 (Table 1). Compounds 4 and 8 also show excellent PSSs (84%-98%) and moderate values (4.7%-9.5%). Switch 9 exhibits the largest bathochromic shifts in both the Z (42 nm) and E (64 nm) forms, compared with 1, and the highest Z E (65.4 6.1%) among all switches. Unfortunately, the overlap between the E and Z absorption bands (Figure S35 in the Supporting Information) resulted in a low PSS for the Z E process (Figure S36 in the Supporting Information). The red-shifts observed in 9 results from the strong ED nature of para-NMe2 and the conjugation of the stator phenyl ring with the hydrazone core. Next, we synthesized the push-pull switch 10 to combine the promising properties obtained when having a paraNO2 group at the rotor, and para-NMe2 group at the stator phenyl groups. The #max of 10-Z is red-shifted by 68 nm (to 435 nm) relative to hydrazone 1 (Figure S37 in the Supporting Information). Upon irradiation with 480 nm light, a PSS480 of > 99 % E is obtained (Figure S40b in the Supporting Information). The quantum yield of the process is significantly higher ( Z E = 46.2 4.2 %) relative to the other derivatives. The 10-E absorption band is bathochromically shifted by 50 nm ( max = 384 nm) relative to 1. The back photoisomerization of 10-E is achieved using 375 nm light source to afford a PSS375 of 96% Z (Figure S40c in the Supporting Information) with 1.1 %. The system shows some photofatigue E Z = 7.4 after 10 switching cycles (Figure S38 and S41b in the Supporting Information). More importantly though, the EOZ isomerization process can be driven using 410 nm light (PSS410 of 90% Z, E Z = 19.4 0.6 %) making 10 the first member of the hydrazone photochromic family that can be solely switched with visible light (Figure S41a in the Supporting Information).25 These results indicate that the push-pull design strategy is a viable one for red-shifting the absorption band of the hydrazone switches.26

(a)

O

O O

N

H

442 nm

N

O H

N N

340 nm or NO2 7-Z

NO2 7-E

(b)

(c)

Figure 2. (a) Light-activated photoisomerization of hydrazone 7; (b) UV-Vis spectra (1 10-5 M) of 7-Z and 7-E isomers in toluene; (c) Photoswitching cycles of 7 in toluene upon alternating the irradiation wavelength between 442 and 340 nm light.



Scheme 2. The proposed conjugation in 5, 8, and 9 showing how EDG and EWG can accelerates the isomerization process . EWG O O H

O

O

O

O

N

H

N

H

N

N N

N

EDG

Kinetic Properties: The thermal isomerization rates of the photochromic hydrazones were measured (in most cases) at an elevated temperature (368K) and the data were extrapolated to room temperature using the Arrhenius and Eyring equations to yield 1/2 and activation barriers, respectively (Figure S58Q65 in the Supporting Information). The extremely long thermal half-lives (year scale) are retained in most of the compounds, except for the ones with EDGs at the stator phenyl group (i.e., 8 and 9), where the rate is accelerated by up to 6 orders of magnitude relative to 1. We hypothesize that the EDG enhances the conjugation between the hydrazone nitrogen and the rotor part of the molecule (Scheme 2, left) by pushing electron density towards the hydrazone core. This process imparts a partial single bond character to the C=N double bond (i.e., the system has a more of an azo character vs. when the phenyl group is not substituted or has an EWG group), which in turn facilitates the isomerization process. That is, in 8 and 9 the isomerization mechanism is no longer inversion as in the rest of the family, but rather rotation around the imine bond. Analysis of the X-ray structures of 6-9 (the Z-isomers were analyzed because we did not obtain crystals of the E-isomers that were suitable for analysis) corroborates this hypothesis as Table 2. Kinetic data for the thermal isomerization of compounds 1 10 in toluene at 298 K. Hydrazonea

kb / s-1

1e

(6.8 0.2) 10-11

2(p-NMe2)f

c 1/2

G‡d / kcal·mol-1

/ year

324 11

31.5 0.1

(1.0 0.1) 10-10

213 7

31.2 0.1

3(m-NMe2)

(1.3 0.1) 10-11

1645 33

32.5 0.1

4(p-OMe)

(3.3 0.2) 10-11

664 44

32.0 0.2

5(p-NO2)

(1.1 0.2) 10-9

20 3

29.8 0.1

6(p-CN)

1033 52

32.2 0.1

(2.1 0.1)

10-11

7(p-NO2)

(1.7 0.1)

10-11

1286 28

32.3 0.1

8(p-OMe)

(5.6 0.2) 10-7

0.039 0.002g

26.0 0.1

9(p-NMe2)

(1.5 0.1) 10-5

0.0015 0.0001g

24.0 0.1

10(p-NMe2, p-NO2)

(1.8 0.2) 10-10

126 11

30.9 0.1

a Thermal relaxation occurs from E Z; b The 1st-order rate constants at 298 K were calculated using the Arrhenius equation; c Half-life at 298 K; d The Gibbs energy of activation was determined using the Eyring equation; e Ref 19a; f Ref 22; g The kinetic study was performed at room temperature.

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the C=N bond is longer in 8 and 9 (1.310 and 1.317 Å, respectively) relative to 6 and 7 (1.304 and 1.299 Å), while the NQN single bond is shorter (1.323 and 1.322 Å for 8 and 9, respectively, vs. 1.334 and 1.342 Å for 6 and 7, respectively). Substitution at the rotor phenyl ring has a less significant effect, in general, on the thermal relaxation rates, and the half-lives are either slightly increased (3, 4) or decreased (2) relative to 1. One exception is 5 where a 2 order of magnitude acceleration in rate is measured. This observation can be explained by the conjugation between the hydrazone NH nitrogen and the nitro group, which imparts a partial single bond character to the C=N double bond (Scheme 2). The X-ray structure of 5 supports this hypothesis as the C=N double bond (1.319 Å) and NQN single bond (1.320 Å) are longer and shorter, respectively, than in 6 and 7, for example. The effect is not as drastic as in 8 or 9 because the rotor phenyl group is not co-planar with the rest of the molecule, and so the conjugation is not as effective. Finally, it is noteworthy that the half-life in 10 is 126 11 years, which is highly unusual for a push-pull system,2 resulting in a red shift in absorption band while maintaining bistability.

(a)

(b)

1

2

5

6

7

8

9

10

Figure 3. (a) The normalized solid-state fluorescence spectra of 1, 2 and 5-10 powders (the absorption maxima in toluene were chosen as excitation wavelengths for each compound); (b) Fluorescence emissions from the powders of hydrazones 1, 2 and 5-10 under 365-nm UV lamp.

Solution and Solid-State Fluorescence Properties: The emission properties of hydrazones 3-10 were first studied in solution using fluorescence spectroscopy (Table 3). The compounds show emissions with varying intensities in toluene at wavelengths (#em) ranging from 450 nm to 560 nm (Figure S66 in the Supporting Information). Hydrazones 2, 4, 8 and 9 bearing EDGs (-OMe or -NMe2) exhibit emission at longer wavelengths in general,


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with no effective interactions between them leading to the observed photophysical properties. Hydrazones 2 and 6 behave similarly in the solid-state (Figures 5a, 5b and S84 in the supporting information). Hydrazones 5 and 9 on the other hand show moderate shifts in emission bands and lower quantum yields than 2, 6 and 8 (Table 3). Again, the crystal structure of these systems helps in understanding this observation. Two molecules of 9 make up the unit cell and stack in a perpendicular fashion where one H-bonded six-membered ring sits on the top of another leading to a cross-shaped pattern (Figure S82 in the supporting information). This loose packing does not lead to complete quenching (quantum yield of ~1%) and only a small red-shift in emission (~15 nm). Hydrazone 5 exhibits a larger bathochromic shift (average of 38 nm) in emission band, and slightly higher quantum yield (~2%). In its crystal structure the rotary phenyl rings of adjacent molecules are located on the same side with a - distance of 3.743 Å (Figures 5c and 5d). This arrangement might explain the bathochromic shift observed in this system, while the loose packing prevents complete quenching.

(d)

(c)

these compounds are similar to the ones measured in toluene, indicating that the same isomerization process is occurring in the solid-state. The absorption bands of 1 and 8 start to broaden and decrease in intensity upon switching cycles, while the peak positions remain unchanged. We ascribe this phenomenon to changes in film morphology (i.e., thickness)31 upon photoisomerization rather than photodegradation or decomposition. On the other hand, the denser packed 5 and 6 show less efficient switching because of the partial overlap of the hydrazone backbone (Figures S89 and S90 in the Supporting Information). No appreciable switching was observed in tightly packed hydrazones 7 and 10 (Figures S91 and S92 in the Supporting Information). The solid-state emission change in these hydrazones also follows the packing mode. The emission toggling in 5, 6, 7 and 10 is not effective because of the low switching efficiency (Figures S89c, S90c, S91c and S92c in the Supporting Information), while in 8 the morphology change in the drop-casted film upon photoswitching diminishes the efficacy of the process (Figures S88c and S88d in the Supporting Information).

CONCLUSIONS

(b)

(a)

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3.743

Figure 5. (a) The packing between two molecules of 6 in the solid-state; (b) The vertical view of the packing in 6; (c) The crystal packing of 5 showing a - interaction (3.743 Å, centroid to centroid distance between the two phenyl rings) formed between two rotary phenyl groups; (d) The stacking of 5 from the vertical view (C-H protons are omitted for clarity).

Solid-State Photoswitching: In addition to being emissive, some of the hydrazones can also undergo photoisomerization in the solid-state. The switching behavior of drop-casted films of the hydrazones were monitored using UV/Vis spectroscopy. It was found that the process is highly dependent on the packing mode observed in the crystal structures. That is, photoswitching is observed for hydrazones that do not have effective packing of their backbones, which matches the empirical observation that free volume is required in the solid-state for efficient isomerization to take place.30 For example, compounds 1 and 8 that are orthogonally stacked (i.e., minimum packing of their backbones, see Figures 4c, 4d and S83 in the supporting information) demonstrate highly efficient back-and-forth photoisomerization (Figures S87 and S88b in the Supporting Information). The UV-Vis absorption bands of the Z isomers and PSSs for

In summary, we systematically studied the effect of ED and EW substituents on the photophysical and switching properties of bistable hydrazone switches.32 Most derivatives show year-scale thermal half-lives, and good absorption band separation, and hence excellent PSSs, and very good photoisomerization quantum yields. The solution phase studies resulted in the following observations: 1) substituting the hydrazone with paraEDGs and para-NO2 group at either the rotor or stator phenyl rings will lead to a red-shift in the absorption profile of the Z isomer. The effect is less pronounced on the E isomer when the substitution is on the rotor phenyl group because of its twist out of the plane of the hydrazone core; 2) enhanced photoisomerization quantum yields are obtained when NMe2 and NO2 functional groups are introduced to the system; 3) derivatizing the rotor phenyl ring has less of an effect on thermal half-lives than substituting the stator phenyl ring; 4) EDGs at the stator phenyl group drastically accelerate the isomerization rate as a result of a hypothesized change in isomerization mechanism, whilst NO2 at the non-coplanar rotor ring results in less significant acceleration; 5) push-pull systems can be used for red-shifting the absorption of both isomers while maintaining the bistability of the switch; and 6) charge transfer from para-NMe2 at the rotary ring is important for efficient emission. The analysis of the crystal structures of the Z isomers shed light on the solid-state packing-dependency of the switching performance, as well as the emission and quenching of the hydrazones in the solid-state. According to this analysis, we found that: 1) the presence of the twisted (out of plane) rotary phenyl ring in the hydrazone (Figure S86 in the Supporting Information) is crucial as it prevents, in general, the systems from stacking effectively, which results in the emergence of solid-state emission and efficient solid-state photoswitching; 2) nitro-substitution at the stator phenyl ring is detrimental to solid-state emission as it results in head-to-tail arrangement and


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Journal of the American Chemical Society quenching; 3) hydrazone 1 is not emissive in the solidstate indicating that EDGs and/or EWGs are required for the hydrazones to be emissive in the solid-state; 4) the enhancement of emission in the solid-state vs solution indicates that rigidification is responsible for the observed phenomenon.29 The insights of this study lay the ground for engineering hydrazone photochromic compounds with specific functions and properties derived from appropriate derivatization(s) of the rotor and/or stator phenyl groups. We are hopeful that these design principles will guide practitioners in their efforts to incorporate these photochromic compounds in a myriad of applications, including but not limited to data storage,33 smart materials,34 molecular machines,35 photopharmacology,8 and super-high resolution fluorescence microscopy,36 among others.37

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on ACS Publications website at DOI: http://pubs.acs.org. General methods, experimental procedures, NMR spectra of key compounds, photoisomerization and kinetic studies, solution and solid-state emission studies (PDF) Crystallographic data for 1-Z (CIF) Crystallographic data for 5-Z (CIF) Crystallographic data for 6-Z (CIF) Crystallographic data for 7-Z (CIF) Crystallographic data for 8-Z (CIF) Crystallographic data for 9-Z (CIF) Crystallographic data for 10-Z (CIF)

AUTHOR INFORMATION Corresponding Author * [email protected]

Author Contributions †These authors contributed equally to this work.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We are grateful to the NSF (CHE-1807428) for the generous support. We gratefully acknowledge Prof. Richard Staples (Michigan State University) for X-ray data.

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Theories Far beyond Their Limits-The Case of the (Boguer-) BeerLambert Law. ChemPhysChem 2016, 17, 1948–1955. (32) These systems are unique in that they are bistable, emissive in the Z form, and switch in the solid-state, which are not characteristics found in the structurally similar acylhydrazone switches (ref 13), for example. (33) (a) Kawata, S.; Kawata, Y. Three-Dimensional Optical Data Storage Using Photochromic Materials. Chem. Rev. 2000, 100, 1777–1788. (34) (a) Roy, D.; Cambre, J. N.; Sumerlin, B. S. Future perspectives and recent advances in stimuli-responsive materials. Prog. Polym. Sci. 2010, 35, 278–301; (b) Ruskowitz, E. R.; DeForest, C. A. Photoresponsive Biomaterials for Targeted Drug Delivery and 4D Cell Culture. Nat. Rev. Mater. 2018, 3, 17087. (35) Leigh, D. A.; Marcos, V.; Nalbantoglu, T.; Vitorica-Yrezabal, I. J.; Yasar, F. T.; Zhu, X. Pyridyl-Acyl Hydrazone Rotaxanes and Molecular Shuttles. J. Am. Chem. Soc. 2017, 139, 7104–7109. (36) (a) Huang, B.; Bates, M.; Zhuang, X. Super-resolution fluorescence microscopy. Annu. Rev. Biochem. 2009, 78, 993 1016; (b) Sydor, A. M.; Czymmek, K. J.; Puchner, E. M.; Mennella, V. Super-Resolution Microscopy: From Single Molecules to Supramolecular Assemblies. Trends Cell Bio. 2015, 21, 730 748; (c) Sahl, S. J.; Hell, S. W.; Jakobs, S. Fluorescence nanoscopy in cell biology. Nat. Rev. Mol. Cell Biol. 2017, 18, 685 701. (37) Lutz, J. F.; Lehn, J. M.; Meijer, E. W.; Matyjaszewski, K. From precision polymers to complex materials and systems. Nat. Rev. Mater. 2016, 1, 16024Q16027.


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TOC 63x44mm (300 x 300 DPI)


Structure Property Analysis of the Solution and Solid-State Properties

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